Reference Electrodes for Use in Aqueous Solutions

Reference Electrodes for Use in Aqueous Solutions. The extensive studies of reference electrodes have been critically surveyed.15 17 

The hydrogen electrode. The hydrogen electrode is discussed first because it is the primary reference electrode used to define an internationally accepted scale of standard potentials in aqueous solution. By convention, the potential of an electrode half-reaction that is measured with respect to the normal hydrogen electrode (NHE also written as SHE, standard hydrogen electrode) is defined as the electrode potential of the half reaction. This convention amounts to an arbitrary assignment for the standard potential of the hydrogen electrode as zero at all temperatures. Thus, there is in effect a separate scale of electrode potentials at each temperature level. 

The hydrogen electrode also is one of the most reproducible electrodes that is available properly prepared electrodes will show bias potentials of less than 10 /lV when compared with one another. 

The hydrogen electrode commonly consists of a platinum foil, the surface of which is able to catalyze the reaction 

Before platinization, electrodes should be cleaned by brief immersion in a solution prepared by combining 3 volumes of 12 M hydrochloric acid with 1 volume of 16 M nitric acid and 4 volumes of water (50% aqua regia). This mixture also can be employed to strip the platinum black from used electrodes. The electrodes are then washed in 16 M nitric acid, rinsed in water, cathodized 

---

The silver-silver chloride reference electrode is one of the most reproducible and reliable reference electrodes for use in aqueous solutions, as well as one of the easiest to construct and use [ii]. For nonaque-ous solutions, the silver-silver ion reference electrode is widely used. It appears to be reversible in all apro-tic solvents except those oxidized by silver ion [ii]. The electrochemistry of silver is discussed in detail in [iii]. 

---